Muscle from humans and animals with myotonia congenita has physiological, structural and biochemical alterations which transcend the loss of CLC-1 channels, including hypertrophy (goats, most humans) or atrophy (mice), alterations in fiber type composition (in particular loss of type IIB fibers, seen in most species with myotonia congenita), and altered amounts of parvalbumin [1,5,7,9,11-13,17,18]. Here, CLCN1 is linked to Thomsen and Becker disease.